1. Field of the Invention
The present invention relates to methods of testing printed circuit board materials for applications involving high-speed communications.
2. Description of the Related Art
A printed circuit board (PCB) is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets that have been laminated onto a non-conductive substrate. Populating the board with electronic components forms a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA). PCBs are rugged, inexpensive, and can be highly reliable. They require more initial layout effort than either wire-wrapped or point-to-point constructed circuits, but are much cheaper, faster, and consistent in high volume production. Many aspects of PCB design, assembly, and quality control are set by standards that are published by the IPC organization
Some PCBs have trace layers inside the PCB and are called multi-layer PCBs. These are formed by bonding together separately etched thin boards. Holes or vias may be formed partially or completely through the PCB by using a drill bit or a laser. Plating or filling a via forms an interconnect that can provide electronic communication between traces in different layers and on the surface.
A communications bus is a subsystem that transfers data or power between computer components inside a computer or between computers. Unlike a point-to-point connection, a bus may logically connect several components over the same set of wires. Most computers have both internal and external buses. An internal bus connects all the internal components of a computer to the motherboard (and thus, the central processing unit and internal memory). These types of buses are also referred to as a local bus, because they are intended to connect to local devices, not to those in other machines or external to the computer. An external bus connects external peripherals to the motherboard.
A modern communications bus transfers data at rates of several gigahertz. At such high speeds, the electronic communications through the bus are subject to dielectric dissipation factor, also known as dielectric loss. Dielectric loss is an intrinsic characteristic of the PCB material. Therefore, the primary approach to controlling the extent of dielectric loss is to carefully select appropriate dielectric materials that will be used in the PCB.
Present approaches taken to qualify materials for PCBs, such as short propagation pulse or corner-corner probing, require expensive equipment and a high level of skill to test properly. Therefore, there is a need for a simple and accurate method for testing a printed circuit board in order to determine whether the dielectric loss of the material is acceptable.